A Bigraphs Paper of Sorts

Bigraphs are an expressive graphical modelling formalism to represent systems with a mix of both spatial and non-local connectivity. Currently it is possible to write nonsensical models, e.g. with a Room nested inside a Person rather than Person nested inside a Room, or to create a hyperedge from what should be a binary link. A sorting scheme can be used to filter badly-formed bigraphs from those that are well formed. While the theory of bigraph sorts is well developed, none of the existing methods leads to a practical implementation. Instead they are based on tables of descriptions or semi-mathematical notations. We look at sorting bigraphs through a practical lens: developing a new sorting language, and show how an extension to the existing theory of bigraphs, in the form of well-sorted interfaces, paves the way for an implementation of well-sorted bigraphs. We discuss the trade-offs of this approach, and show how it allows sorts to be specified for existing bigraph models found in the literature.